This application claims priority from Japanese Patent Application No. 2001-012947, filed on Jan. 22, 2001, the disclosure of which is incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to chemically amplified resist materials having a markedly high alkali dissolution contrast before and after exposure, high sensitivity, high resolution and, in particular, excellent reproducibility as a fine pattern forming material in the fabrication of ultra LSI; and a pattern forming method using the material.
2. Description of the Related Art
With a recent tendency to higher integration and higher operation speed in LSI, finer pattern rules are requested. Under such circumstances, far-ultraviolet lithography is regarded promising as microfabrication technology of the next generation. Particularly, materialization of photolithography using a KrF excimer laser light (wavelength: 248 nm) or ArF excimer laser light (wavelength: 193 nm) as a light source is strongly desired as a technique indispensable for micropatterning of a size of 0.3 xcexcm or less.
In resist materials for KrF excimer laser lithography, polyhydroxystyrene having a practical level of transmittance and etching resistance is incorporated as a standard base resin. For resist materials for ArF excimer laser lithography, on the other hand, use of polyacrylic or polymethacrylic acid derivatives or polymers containing an aliphatic cyclic compound in the backbone thereof are under investigation. Fundamentally, in either case, some or all of alkali soluble moieties of an alkali soluble resin are protected with an acid eliminative group. The overall performance of a resist material is regulated by selecting a proper acid eliminative protecting group or incorporating, in addition to the resin, at least one low molecular component having a necessary function as desired.
One of the typical functional low molecular components to be added to a resist material is a compound group called xe2x80x9cphotoacid generatorxe2x80x9d. Photoacid generators having various structures are proposed for KrF excimer laser lithography. Since photoacid generators for ArF excimer laser lithography are limited from the viewpoints of photoacid generation efficiency, intensity of the acid generated and far ultraviolet absorption (i.e. transmittance), the photoacid generators proposed for KrF excimer laser lithography include onium salts capable of generating an acid of high intensity (see for example, F. M. Houlihan, et al., Proc. SPIE 3678, 264-274(1999); Y. Uetani, et al., Proc. SPIE 3678, 510-517(1999)) or an onium or non-onium salt based photoacid generator having an increased transmittance (see, for example, Japanese Patent Provisional Publication Nos. 10-62995/1998 (U.S. Pat. No. 6,150,068), 10-142777/1998, 10-319581/1998, 10-133371/1998, 10-73912/1998, 10-48814/1998).
Resists for ArF excimer laser lithography are required to have a sufficiently high sensitivity to prevent a deterioration of a lens glass material which presumably occurs upon mass production owing to high energy beams of the ArF excimer laser, high transparency in an ArF excimer laser (wavelength: 193 nm) region and high PED (Post Exposure Delay) stability. Low PED stability is one of the largest obstacle for mass production. In spite of many reports on a lowering mechanism of PED stability of a resist for KrF excimer laser lithography which resist is environmetally unstable (see W. Hinsberg, et al., J. Photopolym. Sci. Technol., 6(4), 535-546(1993)) and PED stabilizers (Japanese Patent Provisional Publication Nos. 5-232706/1993 (U.S. Pat. No. 5,580,695), 5-249683/1993, 7-252214/1995 (U.S. Pat. No. 5,569,784) and 10-20504/1998 (U.S. Pat. No. 5,972,559)), there are almost no reports on a PED stabilizer for a resist suited for ArF excimer laser lithography which resist is more environmetally unstable. There is accordingly a demand for the development of means for resolving this problem.
Under a tendency to finer pattern rules, a resist material having high PED stability, high transmittance, high sensitivity and high resolution is demanded.
With the foregoing in view, the present invention has been made. An object of the present invention is to provide (1) a PED-stabilizer-containing resist material having high sensitivity and high resolution as well as sufficient PED stability; and (2) a pattern formation method using the resist material.
With a view to attaining the above-described object, the present inventors have proceeded with an extensive investigation. As a result, it has been found that at least one compound selected from thiol derivatives, disulfide derivatives and thiolsulfonate derivatives each being a chain transfer agent which is used upon radical polymerization and functions as a radical trap agent is useful as a PED stabilizer to be incorporated in a resist material; particularly, a resist material containing at least one compound selected from thiol derivatives, disulfide derivatives and thiolsulfonate derivatives free of a carbon-carbon double bond has high transmittance, high sensitivity and high resolution; and this resist material is markedly effective for accurate microprocessing, leading to the completion of the present invention.
In one aspect of the present invention, there is thus provided a resist material comprising at least one compound selected from thiol derivatives, disulfide derivatives and thiolsulfonate derivatives. This resist material may further contain a dissolution inhibitor and/or surfactant.
In another aspect of the present invention, there is also provided a pattern forming method, which comprises steps of applying the resist material to a substrate; after a heat treatment, exposing the resist material to a high energy beam or electron beam through a photomask; and after an optional heat treatment, developing the resist material with a developer.
The resist material of the invention is responsive to high energy beams. Owing to excellent sensitivity, resolution, etching resistance and storage stability, it is useful for microprocessing by electron beams or far ultraviolet rays. In particular, small absorption thereof at an exposure wavelength of ArF excimer laser or KrF excimer laser facilitates formation of patterns which are minute and moreover, perpendicular to a substrate.